The present invention relates to floor maintenance equipment and, more particularly, to a floor screening attachment and a dust collection system for a floor finishing machine.
As a result of traffic induced wear, wood floors must be periodically refinished. Before the new finish is applied, the existing finish is sanded lightly or screened to promote adhesion of the new and old finishes. Screening is typically performed with a rotary floor machine of the type used for buffing, scrubbing, polishing, and a number of other floor maintenance operations. Referring to FIG. 1, typically, a floor machine 10 comprises a chassis 12 with an attached operator control handle 14. To facilitate moving the machine 10, a pair of wheels 16 is attached to the chassis 12 supporting the floor machine 10 when it is tipped in the direction of the handle 14. A large diameter circular pad driver 18, located under the chassis 12, is connected to and rotated by a drive shaft 24 that is powered by a motor 20 and gear train 22 mounted in the chassis 12. The pad 26 that performs the polishing, buffing, or other floor care operation is trapped between the pad driver and the floor. Friction between the pad driver 26 and the pad causes the pad to rotate with the pad driver 18. For floor screening, the “pad” or screen 26 comprises an abrasive coated open mesh cloth having the appearance of window screen. Typically, the pad driver 18 used with a screen 26 is faced with felt to provide a resilient backing for the screen 26. Slippage between the felt face of the pad driver 18 and the screen 26 erode the abrasive coating of the screen 26. The life of the abrasive on the side of the screen in contact with the pad driver 18 may be reduced by up to 50%. Since both sides of the screen 26 may be used to abrade the floor, slippage between the screen and pad driver results in a substantial increase in the cost of abrasives required to perform a screening operation.
A second problem inherent in floor screening is the production of a large quantity of fine sanding dust. The dust can be controlled and collected with a wet screening process where water is spread on the floor prior to screening. The dust produced by screening mixes with the water to form a slurry that is removed from the floor by mopping. However, the slurry is difficult clean and its presence on the floor surface obscures the surface making it difficult to judge the progress and quality of the screening operation. For these reasons, floors may be screened while dry. However, the dry screening dust easily becomes airborne and must be cleaned from any horizontal or inclined surface in the vicinity of the screening project. Further, the fine airborne finish particles produced by screening may present a health hazard.
To reduce the airborne dust produced by screening, specialized floor machines with dust collection systems have been devised. Typically, the dust collection system comprises an industrial vacuum cleaner connected to a shroud enclosing the top and the perimeter of the pad driver of the special machine. A special floor machine with a dust collection system may be justifiable for floor refinishing contractors, but many facilities have floor machines that are not equipped for dust collection and a special machine is not justifiable for periodic floor refinishing projects. Further, the quantity and fine nature of the dust produced by screening limits the effectiveness of the typical dust collection system. First, the felt pad driver used for screening comprises random fibers and has limited porosity. Air passages in the felt will quickly plug when air laden with screening dust is drawn through the felt. Since air cannot be drawn through the pad driver without frequent cleaning, the dust becomes trapped in the mesh of the screen and dust collection is only effective when the dust leaks from the edges of the screen disk. In addition, industrial vacuum cleaners rely on a dry filter element that traps particles on the surface of the element when air is drawn through pores of the filter medium. The fine dust produced by screening rapidly plugs the pores of the filter medium and the filter element must be frequently changed or cleaned if the vacuum cleaner is to continue to function.
James et al., U.S. Pat. No. 5,922,093, disclose an ultra-filtration vacuum system that includes multiple liquid and dry filtering stages. Contaminated air drawn into the cannister of the vacuum is directed into a cyclonic air stream that separates large particles and debris from the air. The separated material collects in a first liquid filter medium in the bottom of the cannister. After cyclonic cleaning, the air passes through a labyrinth filter and is injected below the surface a second liquid filter medium. The air forms bubbles that rise to the surface of the liquid where many of the bubbles collapse. The air and liquid are then dispersed in a dispersion chamber. Particles entrained in the air are wetted by the liquid and a combination of cyclonic action and baffles in the dispersion chamber separate the mixture of liquid and wetted particles which flows back into the second liquid filter medium. Particulates remaining entrained in the air are filtered by a final dry filter element. While the vacuum system throughly filters the air, it is complex and not well suited to handling large quantities of fine dust produced by floor screening. Cyclonic cleaning relies on centrifugal force to separate heavy particles and debris from the air stream but is of limited usefulness for removing the fine, light weight particles produced by floor screening. When used for floor screening, the intermediate labyrinth filter would be exposed to essentially unfiltered air and subject to rapid plugging by the screening dust. Injecting contaminated air into a liquid filter media is an effective method of filtering out fine particles, but the volume of liquid in the second liquid filter stage is limited by the necessary equipment and the presence of the first stage filter in the cannister and would rapidly reach its capacity of particulate matter when exposed to the volume of dust. produced by screening.
If the finish is severely worn, floor screening may not be sufficient to prepare the floor for refinishing. In this case, as with newly installed floors, sanding the wood of the floor may be necessary to prepare the surface for the application of the finish. Floor sanding is performed with large belt or drum sanders. Like floor screening, floor sanding creates substantial quantities of dust. As is the case with floor screening, the large quantity of dust will rapidly plug a dry filter of a dust collection system. In addition, the presence of wood in the sanding dust causes foaming in a liquid filter medium severely limiting its effectiveness. Anti-foaming chemicals can reduce the foaming, but the chemicals are only partially effective. Further, adding chemicals to the liquid filter medium significantly increases the cost of floor finishing because the large quantity of dust requires the liquid medium and the anti-foaming chemicals be frequently replaced.
What is desired, therefore, is an apparatus for converting a standard floor machine to a floor screening machine and an effective, large capacity dust collection system suitable for floor screening and sanding operations.